The invention applies to the field of optoelectronic systems for detecting electromagnetic pulses. These systems in particular equip aerial platforms (carrier airplanes, combat airplanes, drones and helicopters), maritime platforms and land-based platforms (combat soldiers, armored vehicles, troop transport, etc.) designed for surveillance and/or combat, as well as laser-guided missiles or bombs.
In particular, the invention is designed for systems particularly of the infrared laser spot tracking (LST) type, laser designation pods (LDP) or self-guided (SG) missile or laser-guided bomb devices. These systems are based on image processing technologies that detect localized electromagnetic pulses, preferably laser pulses.
For example, FIG. 1 illustrates one example application of the invention involving different players: a combat soldier equipped with binoculars, a tank, and an airplane equipped with a missile or bomb. The combat soldier on the ground designates a target to be processed to an airborne support fleet, for example a target to be eliminated by the fleet. To that end, the combat soldier designates the target using a laser designator that comprises a laser source capable of illuminating the target so as to guide ammunition or a weapon, such as a bomb or missile, or to facilitate the targeting of a weapon or light ammunition. The laser designators thus supply information that is useful in targeting the laser-guided ammunition, such as missiles or bombs. Such airborne ammunition includes a so-called self-guided device comprising a spot laser system and means (deviation indicator) measuring the deviation or error between the target and the trajectory of the ammunition. Thus, this airborne ammunition detects the spot laser, the frequency of which is very specific, and adjusts its trajectory based on that spot laser. Owing to spot laser detection algorithms, then the enslavement of the trajectory based on the detected spot laser, the ammunition reaches the target with a very high precision, for example less than 1 m.
The airborne fleet must know the precise position of the target, since the receiving cone of a bomb is limited.
To detect these streams of electromagnetic pulses, pulse detectors exist called quadrant detectors. This type of detector operates continuously. The spot of the electromagnetic pulses on the target is imaged on the quadrant detector. Then, thresholding is done so as to detect the useful signal with respect to the noise using means for processing signals acquired by the quadrant detectors. The latter parts then calculate the respective weight of the image of the illumination spot on each quadrant, i.e., the proportion of the image of the illumination spot on each quadrant.
Such a quadrant detector is connected to means for processing information transmitted by it, for example calculating the ratio of the weights on each quadrant of the illumination spot. These processing means make it possible to calculate the direction of the target that must be followed by ammunition or a guided weapon to reach it. To that end, from direction information, the navigation means of the ammunition connected to the processing means seek to balance the signals over all of the quadrants, which amounts to centering the line of sight on the target.
A laser guiding device for guiding a missile toward the target includes such quadrant detectors and information processing means so as to transmit, for example to the missile, the direction to be followed as far as the target.
One drawback of such a device is that the precision depends on the location of the target in the field of vision and is not constant over the entire field of vision. Thus, it may be excellent at the center of the field, but mediocre at the edge of the field of vision.
In order to increase the precision of the guidance, the electromagnetic pulse detectors include matrix detectors having more pixels than a quadrant detector, for example 100 pixels×100 pixels.
For such devices, the spot corresponding to an illumination pulse is imaged on a single pixel of the detector or on four pixels, thereby improving its location precision. In that case, these devices do not include weighting steps and directly provide the location of the pixel imaging the illumination spot, and consequently the direction of the target.
However, these detectors have an integration time that is substantially equal to a millisecond and operate at 1 kHz, thereby causing an increase in the noise in the detected signal.
Consequently, this type of detector does not perform as well in terms of signal-to-noise ratio, but has an instantaneous field of view (IFV) that is much better than quadrant detectors.